The focus now turns to his stored semen and that of four other dead rhinos, as well as the perfection of in vitro fertilization techniques and the critical need to keep the remaining two females alive.

Whatever happens, conservationists hope the lessons learned in the endeavor can be applied to other critically endangered species.

The 45-year-old Sudan, who won widespread affection last year with his listing as "The Most Eligible Bachelor in the World" on the Tinder dating app in a fundraising effort, was euthanized on Monday after "age-related complications," researchers said Tuesday.

In his death, the world saw the shadow of extinction approach before their eyes. "Utter tragedy today," British Foreign Secretary Boris Johnson tweeted. "We can't just sit back and watch more species disappear."

The rhino "stole the heart of many with his dignity and strength," said the Ol Pejeta Conservancy in Kenya, where Sudan lived. It said his condition had "worsened significantly," to the point where he was no longer able to stand. His muscles and bones had degenerated and his skin had extensive wounds, including a deep infection on his back right leg.